Cook potatoes: Add a steamer basket to a small saucepan and fill with water until it's ½-inch below the basket. Cover and bring to a boil over medium-high heat. Add potatoes and steam until soft when poked with a fork, about 10 minutes. Drain and let cool slightly.
1 lb yellow potatoes, cubed (½-inch)
Cook onion and spices: Meanwhile, warm oil in a skillet over medium-high heat. Add onion, sauté until soft, 5 to 7 minutes. Reduce heat to medium. Add cumin seeds, cook for 1 minute. Add curry powder, coriander, and turmeric. Cook stirring frequently, until fragrant, 1 to 2 minutes.
1 tablespoon grapeseed oil, ½ cup red onion, minced, 1 teaspoon cumin seeds, ¾ teaspoon Madras curry powder, ¼ teaspoon coriander, ¼ teaspoon ground turmeric
Mix: Transfer the onion and spice mixture into a large bowl. Whisk in yogurt and lemon juice. Add chickpeas, celery, bell pepper, scallions, and potatoes. Stir well to mix. Season with salt.
½ cup Greek yogurt, 1 tablespoon lemon juice, 1 (15 oz/14 fl oz/398 ml) can chickpeas, rinsed, 2 ribs celery, diced, ¾ cup diced red bell pepper, 2 scallions/green onions, thinly sliced, ½ to ¾ teaspoon fine sea salt
Make slaw: In a small bowl, toss apples, cilantro and lemon juice.
2 apples, peeled and cut into matchsticks, 1 to 2 tablespoons chopped cilantro, 1 to 2 tablespoons lemon juice
Assemble: Tuck a piece of lettuce into each pita, then scoop in filling. Top with apple cilantro slaw.
6 leaves lettuce, 6 pitas